In a posting on his GM blog on Thursday, Lutz said those "spewing virtual vitriol" at him for minimizing the threat of climate change were "missing the big picture."

"What they should be doing in earnest is forming opinions, not about me but about GM and what this company is doing that is ... hugely beneficial to the causes they so enthusiastically claim to support," he said in a posting titled, "Talk About a Crock."

GM, the largest US automaker by sales and market share, has been trying to change its image after taking years of heat for relying too much on sales of large sport-utility vehicles like the Hummer and not moving faster on fuel-saving hybrid technology.

"My thoughts on what has or hasn't been the cause of climate change have nothing to do with the decisions I make to advance the cause of General Motors," he wrote.

Lutz said GM was continuing development of the battery-powered, plug-in Chevy Volt and other alternatives to traditional internal combustion engines.

GM is racing against Toyota Motor Corp to be first to market a plug-in hybrid car that can be recharged at a standard electric outlet.

Lutz has previously said GM made a mistake by allowing Toyota to seize "the mantle of green respectability and technology leadership" with its market-leading Prius hybrid.

A 40-year auto industry veteran who joined GM earlier in the decade with a mandate to shake up its vehicle line-up, Lutz is no stranger to controversy.

As part of a campaign against higher fuel economy standards, Lutz wrote in a 2006 blog posting that forcing automakers to sell smaller cars would be "like trying to address the obesity problem in this country by forcing clothing manufacturers to sell smaller, tighter sizes."

Automakers ended their opposition to higher fuel standards in 2007 when it became clear that proposed changes would become law with or without their support.

In December, US President George W. Bush signed a law mandating a 40 percent increase in fleetwide fuel economy by 2020, the first substantial change in three decades.